Contact lenses, like eyeglasses or vision surgery, can correct nearsightedness, farsightedness and astigmatism. About 20 percent of Americans who need vision correction for these refractive errors wear contact lenses. While some people enjoy making a fashion statement with eyeglasses, others prefer their appearance without them. Contact lenses offer the ability to be glasses-free without expensive vision surgery. Contacts also provide a wider field-of-view than glasses, which is great for driving and sports. Contact lenses have been around for more than a hundred years, and today just about everyone can wear contact lenses. If you were told in the past that you couldn’t wear contacts, odds are you can today. There are more convenient and healthy contact lens options than ever, including many contact lenses that can correct astigmatism.
The first step in being fitted for contacts is to see an eye doctor for a comprehensive eye exam. In the United States, contact lenses are considered medical devices and must be prescribed and properly fitted by an eye care professional (ECP). Your ECP will evaluate your visual needs, your eye structure, and your tears to help determine the best type of contact lenses for you.
Contact lenses are classified according to:
• The lens material
• The lens design
• How long you can wear them without removal
• How long you can use them before they should be discarded
There are four types of contact lenses, based ion the material they are made of:
Soft lenses are thin lenses made of gel-like, water-containing plastics. More than 90 percent of contact lenses worn today are soft lenses. They generally are easy to adapt to and cover the entire cornea (the clear front surface of your eye).
Gas permeable lenses (also known as GP, RGP or rigid gas permeable lenses) are smaller lenses made from rigid, waterless plastics. In many cases, GP lenses provide sharper vision than soft lenses.
Hybrid lenses have a central GP zone, surrounded by a border made of a soft lens material. These lenses provide the crisp optics of a GP lens, with comfort that rivals soft lenses.
Hard lenses are similar in appearance to GP lenses, but they are made of rigid plastic that is not permeable to oxygen. Hard lenses have virtually been replaced by GP lenses and rarely are prescribed today.
The most popular contact lenses worn today are a special type of soft lens called silicone hydrogel lenses. These lenses allow more oxygen to pass through them than conventional soft lenses, reducing the risk of contact lens discomfort and complications.
There are two types of contact lenses based on recommended wearing time:
Daily wear contacts — Lenses that must be removed nightly
Extended wear contacts — Lenses that can be worn overnight
“Continuous wear” is a term that’s sometimes used to describe 30 consecutive nights of lens wear — the maximum wearing time approved by the FDA for certain brands of extended wear lenses.
Even with proper care, contact lenses (especially soft contacts) should be replaced frequently to prevent the build-up of lens deposits and contamination that increase the risk of eye infections. Soft lenses have these general classifications, based on how frequently they should be discarded:
Daily disposable — Discard after a single day of wear
Disposable (used for daytime wear) — Discard after two weeks Disposable (used for overnight wear) — Discard after one week
Continuous wear (used for 30-day wear) — Discard monthly
Planned replacement — Discard at intervals of one to three months
Gas permeable contact lenses are more resistant to lens deposits and do not need to be discarded as frequently as soft lenses. Often, GP lenses can last a year or longer before they need to be replaced.
Several contact lens designs are available to correct various types of vision problems:
Spherical contact lenses are the most common design. Spherical soft lenses correct nearsightedness and farsightedness. Spherical GP lenses can correct nearsightedness, farsightedness and astigmatism.
Toric lenses (soft and GP) have multiple lens powers to correct astigmatism. Bifocal and multifocal contact lenses (soft and GP) contain different zones for near and far vision to correct presbyopia.
Orthokeratology (ortho-k) and corneal refractive therapy (CRT) lenses are specialty GP lenses designed to reshape the cornea during sleep and temporarily correct myopia and other refractive errors for clear vision without glasses or contacts during the day.
Custom soft and GP lens designs also are available for hard-to-fit eyes, including eyes with keratoconus.
Colored Lenses: Soft contact lenses are available in a variety of colors that can enhance the natural color of your eyes — to make your green eyes even greener, for example. Other colored lenses can change the color of your eyes entirely — from brown to blue, for example.
Special-Effect Lenses: Also called theatrical, gothic, Halloween or costume lenses, these soft lenses take coloration one step further to make you look like a cat, a zombie, or another alter-ego of your choice.
Prosthetic Lenses: These custom-made color contact lenses are used to restore a natural appearance to eyes that have been disfigured by injury or disease. In cases when only one eye is affected, a prosthetic lens is designed to closely match the appearance of the normal eye.
The first step in finding the best contacts for you is to schedule a comprehensive eye exam and contact lens consultation with your eye doctor. During this exam, your doctor will make sure your eyes are healthy enough to wear contact lenses and advise you regarding what to expect when wearing contacts.
Next is the contact lens fitting itself. Detailed measurements of your eyes are taken, and trial lenses often are applied to achieve the best possible fit and determine if you can comfortably wear contacts.
A contact lens fitting takes several office visits and you will be asked to return a number of times to make sure the lenses continue to fit properly and remain comfortable after prolonged periods of wear. In some cases, changes of lens size or design are needed before the fitting process is complete.
Your prescription for contact lenses is written only after the contact lens fitting process is completed and your doctor is satisfied with the long-term fit of your lenses and how well your eyes tolerate contact lens wear.
Caring for your contact lenses — cleaning, disinfecting and storing them — is much easier than it used to be. In most cases today, only a single care solution is required for cleaning, rinsing and storing your lenses. And if you choose daily disposable soft lenses, routine lens care can be eliminated altogether. Your eye doctor or contact lens technician will teach you how to apply, remove and care for your lenses during your contact lens fitting.
Gas permeable contact lenses (also called rigid gas permeable, RGP or GP lenses) are rigid contact lenses made of silicone-containing compounds that allow oxygen to pass through the lens material to the eye. Though not as popular as soft contact lenses, GP lenses offer a number of advantages.
Advantages of gas permeable lenses
More oxygen for the eye. Gas permeable lenses allow more oxygen to reach the front surface of the eye (cornea), reducing the risk of eye problems from inadequate air supply (hypoxia). This advantage of GP lenses is due to several reasons:
1.) GP lens materials are more permeable to oxygen than many soft lens materials (though new “silicone hydrogel” soft lenses are comparable to GPs in oxygen transmission).
2.) Gas permeable lenses are smaller in diameter than soft lenses, so they cover up less of the front surface of the eye.
3.) GP lenses hold their shape and move on the eye with each blink. This movement pumps oxygen-containing tears under the lens. Soft lenses move only minimally with blinks, so little or no tears circulate under the lenses to improve oxygen supply to the cornea.
GP lenses provide sharper vision.
Gas permeable lenses are custom-machined to a smooth surface and maintain their shape on the eye, enabling them to provide sharper vision than soft lenses, which can fluctuate in shape and clarity if they start to dry out. GP lenses also provide a more stable and accurate correction of astigmatism.
Gas permeable lenses last longer. GP lenses are rigid, so there’s no worry about ripping or tearing them. They also are easier to keep clean and don’t need to be replaced frequently like soft lenses. With proper care, a single pair of GP lenses can last a year or longer, so even though they cost more per pair, gas permeable lenses can be a better value than soft lenses in the long run.
GP lenses may slow the progression of nearsightedness. In addition to their other advantages, some research suggests that wearing gas permeable lenses may slow the progression of myopia (nearsightedness) in some children. GPs are also used for orthokeratology, where specially designed contacts are worn during sleep to reshape the cornea and improve vision.
Disadvantages of gas permeable lenses
So why aren’t GP lenses more popular? Compared with soft lenses, potential disadvantages of GP lenses include:
Need for adaptation
Unlike soft contact lenses that usually are comfortable immediately, it typically takes a week or longer for your eyes to adapt to wearing gas permeable lenses. Initially, you may be able to wear GP lenses only a few hours per day. But if you can tough it out for those first few days, you may be pleasantly surprised at how comfortable GP lenses become. Many people who switch from soft lenses to gas permeable lenses say that after an initial adaptation period, GP lenses are more comfortable than soft lenses and their vision is noticeably clearer.
Not suitable for part-time wear
To fully adapt to GP lenses and to stay comfortable wearing them, you have to wear them every day. If you stop wearing them for several days, they typically will be less comfortable when you resume wear and you will need to re-adapt to the lenses. If you want to wear contact lenses only on a part-time basis, soft lenses usually are a better choice.
Increased risk of lens loss
Because they are smaller than soft lenses, gas permeable lenses can dislodge from your eyes during contact sports or if you rub your eyes aggressively.
Vulnerability to sand and dust
Because GP lenses are smaller in diameter than soft lenses and are designed to allow tears to flow behind the lenses, it’s possible sand or dust can get under your lenses at the beach or on a windy day. You can minimize this risk by wearing wrap-style sunglasses outdoors. Higher lens replacement costs Unlike soft lenses, gas permeable lenses are custom-made for your eyes and therefore are more expensive to replace if you lose them. Also, it can take up to a week to receive replacement GP lenses. So it’s a good idea to purchase a spare pair to avoid the inconvenience of being without your GP lenses if you lose or break one.
Hybrid contact lenses are innovative lenses that have a GP central optic zone, surrounded by a “skirt” of soft lens material. These lenses are designed to provide the crisp, clear vision of gas permeable lenses and wearing comfort that rivals that of soft contact lenses. Like soft lenses, hybrid contact lenses are larger in diameter than GP lenses for greater wearing comfort and greater stability on the eye with less risk of lens loss.
During your contact lens consultation and fitting, your eye care provider can demonstrate for you the comfort and clarity of both GP and hybrid contact lenses.
A number of eye conditions can make wearing contact lenses more challenging. These conditions include:
- dry eyes
- giant papillary conjunctivitis (GPC)
- post-refractive surgery (such as LASIK)
If you have any of these conditions, you still might be able to wear contacts quite successfully. It just means you may need to be fitted with lenses specially designed for your condition or “hard-to-fit” eyes.
Astigmatism is a very common condition where the curvature of the front of the eye isn’t symmetrical in all meridians (like a baseball). Instead, the cornea is shaped more like a football or the back of a spoon — with one meridian (from 12 o’clock to 6 o’clock, for example) being relatively flat and the meridian 90 degrees away (3 o’clock to 9 o’clock) being significantly steeper. In most cases, you can still wear contacts successfully if you have astigmatism — you just need a different kind of lens.
Soft contact lenses specially designed to correct astigmatism are called “toric” lenses. Toric soft lenses have different corrective powers in different lens meridians, and design features to prevent the lens from rotating on the eye. These stabilizing features keep the lens powers aligned in front of the proper meridians of the eye for clear vision. In some cases, toric soft lenses may rotate too much on the eye, causing blur. If this happens, other brands with different stabilizing features can be tried.
If rotation of toric soft lenses continues to be a problem, gas permeable (GP) lenses (with or without a toric design) also can correct astigmatism.
Dry eye is perhaps the most common cause of contact lens discomfort. Symptoms of dry eye syndrome include:
- a gritty, dry feeling
- a burning sensation
- a feeling that something is “in” your eye (called a foreign body sensation)
- eye redness (especially later in the day)
- blurred or fluctuating vision
If you have dry eyes, the first step is to treat the condition. This can be done a number of ways, including frequent use of artificial tears or other eye drops, use of nutritional supplements, and a doctor-performed procedure called punctal occlusion to close ducts in your eyelids that drain tears away from your eyes. Once the dry eye condition is treated and symptoms are reduced or eliminated, contact lenses can be tried.
Certain soft contact lens materials may work better than others for dry eyes, and there are even some contact lenses specially designed for people with dry eyes. Also, rigid gas permeable lenses sometimes are better than soft lenses for dry eyes since GP lenses don’t dry out the way soft lenses can.
Replacing your contacts more frequently and reducing your wearing time each day also can reduce dry eye symptoms associated with contact lens wear. Removing your contacts and wearing glasses for specific tasks such as extended computer use also can help.
Giant papillary conjunctivitis (GPC) is an inflammatory reaction on the inner surface of the eyelids. One cause of GPC is protein deposits on soft contact lenses. (These deposits are from components of your tear film that stick to your lenses and become chemically altered.) Usually, changing to one-day disposable contact lenses will solve this problem, since you just throw these lenses away at the end of the day before protein deposits can accumulate on them.
Gas permeable lenses also are a good solution, as protein deposits don’t adhere as easily to GP lenses, and lens deposits on GP lenses are more easily removed with daily cleaning.
In some cases of GPC, using a medicated eye drop for a period of time may be required to reduce the inflammation before you can resume wearing contact lenses.
Keratoconus is a relatively uncommon eye condition where the cornea becomes thinner and bulges forward. The term “keratoconus” comes from the Greek terms for cornea (“kerato”) and cone-shaped (“conus”). The exact cause of keratoconus remains unknown, but it appears that genetics and oxidative damage from free radicals play a role. Gas permeable contact lenses generally have been the treatment of choice for mild and moderate keratoconus. Because they are rigid, GP lenses can help contain the shape of the cornea. They also can correct vision problems caused by keratoconus that cannot be corrected with eyeglasses or soft contacts. In some cases, a soft contact lens is worn under the GP lens for greater comfort. This technique is called “piggybacking.” Another option for some patients is a hybrid contact lens that has a GP center, surrounded by a “skirt” of comfortable soft lens material.
Many Americans each year choose to undergo LASIK or other elective refractive surgery to correct their eyesight. Sometimes, vision problems remain after surgery that can’t be corrected with eyeglasses or a second surgical procedure. In these cases, gas permeable contacts often can restore visual acuity and eliminate problems like glare and halos at night. GP lenses also are used to correct vision problems after cornea transplant surgery, including irregular astigmatism that cannot be corrected with eyeglasses.
GP lenses prescribed after LASIK and cornea transplants sometimes have a special design called “reverse geometry” to better conform to the altered shape of the cornea. The back surface of these lenses is flatter in the center and steeper in the periphery. (This is the opposite of a normal GP lens design, which is steeper in the center and flattens in the periphery.)
Presbyopia is the normal loss of ability to focus on near objects that occurs in middle age. Nearly everyone experiences some symptoms of presbyopia by ages 45 to 50. Today, there are many designs of bifocal and multifocal contact lenses to correct presbyopia. Another option for presbyopia is monovision — wearing a contact lens in one eye for distance vision and a lens in the other eye that has a modified power for near vision.
During your contact lens fitting, your eye doctor can help you decide whether bifocal/multifocal contact lenses or monovision is best for you.
Fitting contact lenses to correct or treat any of the above conditions generally takes more time than a regular contact lens fitting. These “hard-to-fit” cases usually require a series of office visits and multiple pairs of trial lenses before the final contact lens prescription can be determined. Also, special-design contact lenses required for these conditions typically are more costly than regular soft contact lenses. Therefore, fees for these fittings are higher than fees for regular contact lens fittings.
If you are interested in wearing contact lenses, call our office to schedule a consultation. Even if you’ve been told you’re not a good candidate for contacts because you have one of the above conditions or for some other reason, we may be able to help you wear contact lenses safely and successfully.
Source: Contacts for Hard-to-Fit Eyes by AllAboutVision.com. Article ©2011 Access Media Group LLC. All rights reserved. Reproduction other than for one-time personal use is strictly prohibited.